Working alone, pump A can empty a pool in 3 hours. Working a

Working alone, pump A can empty a pool in 3 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool?

A. 72
B. 75
C. 84
D. 96
E. 108

OA A

Source: Magoosh

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Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 am; Location: Grand Central / New York; Thanked: 470 times; Followed by:34 members

by Jay@ManhattanReview » Tue Feb 26, 2019 10:11 pm

BTGmoderatorDC wrote:Working alone, pump A can empty a pool in 3 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool?

A. 72
B. 75
C. 84
D. 96
E. 108

OA A

Source: Magoosh

Work done by pump A and B together in 1 hour = 1/3 + 1/2 = 5/6 part of the pool

Thus, it takes 1 / (5/6) = 6/5 hours or (6/5)*60 = 72 minutes to empty the pool

The correct answer: A

Hope this helps!

-Jay
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swerve: Legendary Member; Posts: 2229; Joined: Sun Oct 29, 2017 2:04 pm; Followed by:6 members

Let the total work be 1

by swerve » Wed Feb 27, 2019 7:06 am

Let the total work be 1
Rate of work A = Total work done/ Total time taken $= 1/3$
Rate of work B = Total work done/ Total time taken $= 1/2$

Total Rate $= 1/2 + 1/3 = 5/6$
In 1 hour work done is $= 5/6$
Time taken to complete the entire work (1) $= 6/5$ hours

$(6/5)*60=72$ minutes.

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